• No results found

Treating Water Using a Perforated Electrode Flow Through Cell

N/A
N/A
Protected

Academic year: 2021

Share "Treating Water Using a Perforated Electrode Flow Through Cell"

Copied!
115
0
0

Loading.... (view fulltext now)

Full text

(1)

http://researchcommons.waikato.ac.nz/

Research Commons at the University of Waikato

Copyright Statement:

The digital copy of this thesis is protected by the Copyright Act 1994 (New Zealand). The thesis may be consulted by you, provided you comply with the provisions of the Act and the following conditions of use:

 Any use you make of these documents or images must be for research or private study purposes only, and you may not make them available to any other person.

 Authors control the copyright of their thesis. You will recognise the author’s right to be identified as the author of the thesis, and due acknowledgement will be made to the author where appropriate.

 You will obtain the author’s permission before publishing any material from the thesis.

(2)

Treating Water Using a Perforated Electrode Flow

Through Cell

Master of Science in Materials and Process Engineering

at

The University of Waikato by

Jayani Hettiarachchi

(3)

Abstract

Perforated Electrode Flow Through cell (PEFT cell) is an undivided electro – chlorination cell designed by the University of Waikato. A new design was developed that consists of two sets of perforated electrodes assembled in a 3D printed casing. The aim of this research was to test the new PEFT cell for chlorine production, trial it for E-coli disinfection and iron and manganese removal by coupling it to a DMI-65 column. Maximum chlorine concentration was achieved at 0.1 mol/L NaCl concentration at a flow rate of 1.8 ml/s at 5 volts

and 10 amps, and a current density of 44 mA/cm2, resulting in a chlorine

concentration of 510 mg/L. Chlorine production increased with increasing salt concentration but decreased with flow rate. Maximum chlorine production rate was at 0.14 mg/s.amp at 7.41 ml/s flow rate. Total inactivation of E-coli bacteria was achieved for all conditions tested. Iron and manganese removals of 92.5% and 90% respectively were achieved for synthetic bore water when the PEFT cell was coupled to a DMI-65 column.

(4)

Acknowledgements

I am sincerely grateful to my supervisor Dr. Mark Lay for his guidance, support and knowledge. It wouldn’t be success if not your helping hand whenever I needed it. I would also like to thank Dr. Graeme Glasgow my second supervisor.

A special thanks to my parents for supporting me financially and to my brother for technical support.

I am also thankful to Lisa Li, Mary Dalbeth and Cheryl Ward of University of Waikato.

I owe you gratitude James Aremu for assenting me in E- coli testing, synthetic bore water preparation and using instruments.

Finally, I am not forgotten my colleagues Safiya, Anu, Sandra, Maria, Tim and

Chawa for their encouragement, advices and enormous support throughout the research.

(5)

Table of Contents

August 2017 ... i

Abstract ... ii

Acknowledgements ... iii

Table of Contents ... iv

List of Figures ... vii

List of Tables ... x 1 Introduction ... 1 1.1 Background ... 1 1.2 Research objectives ... 2 1.3 Thesis outline ... 3 2 Literature Review ... 1 2.1 Introduction ... 1 2.2 Water ... 1 2.3 Water sources ... 2 2.3.1 Surface waters ... 2 2.3.2 Ground waters ... 3 2.4 Water contaminants ... 5 2.5 Water standards ... 9 2.6 Treating water ... 15 2.6.1 Screening ... 17 2.6.2 Sedimentation ... 18 2.6.3 Coagulation ... 18 2.6.4 Filtration ... 19

2.6.4.1Rapid gravity filtration ... 19

2.6.4.2Slow sand filtration ... 19

2.6.4.3Membrane filtration ... 20 2.6.5 Adsorption ... 20 2.6.6 Ion exchange ... 21 2.6.7 Disinfection ... 21 2.7 Disinfection ... 21 2.7.1 Physical disinfection ... 22 2.7.2 Chemical disinfection ... 22 2.7.3 Chlorination ... 23

(6)

2.7.5 UV radiation ... 27

2.8 Contaminant removal ... 31

2.8.1.1Filtration ... 33

2.8.1.2DMI – 65 ... 35

2.9 PEFT (Perforated Electrode Flow Through) cell ... 38

2.9.1 Electro-chlorination ... 38

2.9.2 Voltage and Current ... 41

2.9.3 PEFT cell for disinfection and iron and manganese removal ... 43

2.10Conclusion ... 43 3 Methodology ... 45 3.1 Materials ... 45 3.2 Equipment ... 45 3.2.1 Palintest Photometer ... 47 3.2.1.1Calibration ... 47

3.2.1.2Test for free chlorine ... 47

3.2.1.3Test for Iron ... 47

3.2.1.4Test for Manganese ... 48

3.3 PEFT cell operation ... 48

3.4 Optimum current, voltage and salt (NaCl) concentration for maximum chlorine production ... 49

3.5 Assess disinfection properties by e – coli counting ... 49

3.5.1 Testing for e – coli ... 49

3.6 Coupling DMI-65 with the PEFT cell to remove iron and manganese ... 50

4 Results and Discussion ... 54

4.1.1 Optimum current, voltage and Salt (NaCl) concentration ... 54

4.1.1.1Short circuiting ... 63

4.1.2 PEFT disinfection properties ... 64

4.1.3 Iron and manganese removal capability in a coupled PEFT cell-DMI-65 column ... 66

5 Conclusions and Recommendations ... 85

5.1 Conclusions ... 85

5.1.1 Chlorine generation ... 85

5.1.2 Disinfection ... 85

(7)

5.2 Recommendations for future work ... 86 References ... 88

(8)

List of Figures

Figure 2.1 Left: Polar water molecule, Right: Hydrogen bonds between

water molecules (commons, 2013; Lodish, 2008) ... 2

Figure 2.2 Global hydrological system (Todd, 2004) ... 4

Figure 2.3 Scanning electron micrograph of Escherichia coli bacteria (Mundasad, 2011) ... 8

Figure 2.4 Coagulation and flocculation (Gregory, 2004) ... 18

Figure 2.5 Cationic polyelectrolyte and Anionic polyelectrolyte ... 19

Figure 2.6 Filtration spectrum of MF, UF and NF (YAMIT Filtration and Water Treatement, n.d.) ... 20

Figure 2.7 Resonance structures of ozone(Chemistry Stack Exchange Inc., 2015) ... 25

Figure 2.8 UV in Electromagnetic Spectrum (LIT UV elektro, n.d.) ... 27

Figure 2.9 UV disrupts nucleotides in DNA (LIT UV elektro, n.d.) ... 28

Figure 2.10 UV reactor installment (Ministry of Health, 2010 ) ... 29

Figure 2.12 Adsorption, Oxidation mechanism of iron and manganese by DMI-65 ... 37

Figure 2.13 Schematic of existing PEFT cell... 41

Figure 3.1 New 3D printed PEFT cell ... 46

Figure 3.2 Schematic of new 3D printed PEFT cell ... 46

Figure 3.3 Suction apparatus ... 50

Figure 3.4 DMI-65 column ... 51

Figure 4.1 PEFT current vs voltage for 0.01 mol/L salt concentration ... 55

Figure 4.2 PEFT current vs voltage for 0.05 mol/L salt concentration ... 55

Figure 4.3 PEFT current vs voltage for 0.1 mol/L salt concentration... 56

Figure 4.4 Comparison of free chlorine production at 0.01 mol/L (0.5844g/L) NaCl concentration under different flow rates ... 57

Figure 4.5 Comparison of free chlorine production at 0.05 mol/L (2.922g/L) NaCl concentration under different flow rates ... 57

Figure 4.6 Comparison of free chlorine production at 0.1 mol/L (5.844g/L) NaCl concentration under different flow rates ... 58

(9)

NaCl concentrations at 1.80 ml/sec flow rate ... 58 Figure 4.8 Comparison of free chlorine production with current at different

NaCl concentrations at 3.95 ml/sec ... 59 Figure 4.9 Comparison of free chlorine production with current at different

NaCl concentrations at 5.81 ml/sec ... 59 Figure 4.10 Comparison of free chlorine production with current at different

NaCl concentrations at 7.41 ml/sec flow rate ... 60 Figure 4.11 Comparison of free chlorine production with current at different

NaCl concentrations at 12.05 ml/sec flow rate ... 60 Figure 4.12 Corrosions inside the PEFT cell ... 61 Figure 4.13 Yellowish color solution resulted in after current flowed

through electrodes ... 62 Figure 4.14 Replaced small metal plates... 62 Figure 4.15 Chlorine production rate at the different NaCl concentrations

and flowrates. ... 63 Figure 4.16 Damaged PEFT cell chamber due to short- circuiting... 64 Figure 4.17 E-coli in untreated lake water samples a) 50% dilution b) 10%

dilution ... 65 Figure 4.18 E-coli testing for treated lake water ... 65 Figure 4.19 a) Iron removal b) Manganese removal at 0.01mol/L (0.5844g/L)

NaCl concentration, 1.80 ml/sec flow rate ... 67 Figure 4.20 a) Iron removal b) Manganese removal at 0.01 mol/L

(0.5844g/L) NaCl concentration, 3.95 ml/sec flow rate ... 68 Figure 4.21 a) Iron removal b) Managanese removal at 0.01 mol/L

(0.5844g/L) NaCl concentration, 5.81 ml/sec flow rate ... 69 Figure 4.22 a) Iron removal b) Manganese removal at 0.01 mol/L

(0.5844g/L) NaCl concentration, 7.41 ml/sec flow rate ... 70 Figure 4.23 a) Iron removal b) Manganese removal at 0.01 mol/L

(0.5844g/L), 12.05 ml/sec flow rate ... 71 Figure 4.24 a) Iron removal b) Manganese removal at 0.05mol/L (2.922g/L),

1.80 ml/sec flow rate ... 73 Figure 4.25 a) Iron removal b) Manganese removal at 0.05 mol/L (2.922g/L),

3.95 ml/sec flow rate ... 74 Figure 4.26 a) Iron removal b) Manganese removal at 0.5mol/L (2.922g/L)

(10)

NaCl concentration, 7.41 ml/sec flow rate ... 76 Figure 4.28 a) Iron removal b) Manganese removal at 0.05 mol/L (2.922g/L)

NaCl concentration, 12.05 ml/sec flow rate ... 77 Figure 4.29 a)Iron removal b) Manganese removal at 0.1 mol/L (5.844g/L)

NaCl concentration, 1.80 ml/sec flow rate ... 79 Figure 4.30 a) Iron removal b) Manganese removal at 0.1 mol/L (5.844g/L)

NaCl concentration, 3.95 ml/sec flow rate ... 80 Figure 4.31 a)Iron removal b) Manganese removal at 0.1mol/L (5.844g/L)

NaCl concentration, 5.81 ml/sec flow rate ... 81 Figure 4.32 a) Iron removal b) Manganese removal at 0.1 mol/L (5.844g/L)

NaCl concentration, 7.41 ml/sec flow rate ... 82 Figure 4.33 a) Iron removal b) Manganese removal at 0.1 mol/L (5.844g/L)

(11)

List of Tables

Table 2.1 Water sources and their contribution to global water availability

(Agnew, 2011) ... 2

Table 2.2 Drinking water Contaminants (Contaminants, 1900; Ministry of Health, 2007) ... 6

Table 2.3 General quality requirements for household water (Health, 2013) ... 10

Table 2.4 Colour scale uses for the individual contaminant grading (Ministry for the Environment, 2004) ... 12

Table 2.5 Overall grade of source water and grade interpretation (Ministry for the Environment, 2004) ... 12

Table 2.6 Keys use to grade source, treatment and distribution (Ministry of Health, 1995, 2001) ... 13

Table 2.7 Total points for the grading (Ministry of Health, 2001) ... 13

Table 2.8 Award merit points for source/ treatment and distribustion criteria (Ministry of Health, 2001) ... 14

Table 2.9 Maximum acceptable values for microbial determinants (Ministry of Health, 2008) ... 14

Table 2.10 Guideline values (GV) for aesthetic determinants (Ministry of Health, 2008) ... 15

Table 2.11 Unit processes and applications (Schutte, 2006) ... 17

Table 2.12 Distinct bands of UV (Akram, 2005) ... 28

Table 2.13 Comparison of drinking water disinfectants (McGuire, 2016) ... 29

Table 2.14 Common ions found in water (Seneviratne, 2007) ... 31

Table 2.15 Advantages and drawbacks of different iron and manganese removal methods (Odell, 2010) ... 34

Table 2.16 Chemical composition, physical properties and operation conditions of DMI-65 (Quantum Filtration Medium Pty Ltd., 2010; Soon Ngai Engineering SDN BHD, n.d.) ... 36

Table 2.17 Commercially available chlorine generators (Fujian Hada Intelligence Technology Co. Ltd., n.d.; MIOX Mixed Oxidant Solution (MOS), n.d.) ... 40

(12)

Table 4.1 Maximum chlorine production of different flow rates at 0.05 mol/L (2.922g/L) NaCl concentration and maximum metal

removals ... 78 Table 4.24 Maximum chlorine production of different flow rates at 0.1

mol/L (5.844 g/L) NaCl concentration and maximum ion

(13)

1 Introduction

1.1 Background

The Earth’s biosphere is enriched with water where it can be found as vapour, liquid or ice. All life forms on Earth depend on water, and ecosystems and livelihoods within a selected environment strongly depends on the available quantities and quality of the water (Young, 1994).

Human population growth projection for 2025 shows rapid growth mainly in developing countries. To maintain the population, demand for clean drinking water will increase globally (Young, 1994). With increasing population and complexity of life style, water use and management is important since ‘control of water is inevitably control of life and livelihood’. Water resource degradation, depletion and pollution led governments and natural resource protecting organizations to institute policies to encourage conservation of water resources and water quality (Strang, 2004).

3.5 million people are killed each year from untreated or poorly disinfected water (World Health Organization, 2001). Failure to supply safe water for human consumption is one of the greatest development failures in this century. It is been analyzed that if no action is taken, 135 million people will die by 2020 due to lack of water quality (Gleick, 2002). Main pathogens present in water are E-coli, camphylobacter, giardia, crytosporidium (Crockett, 2007). Recently in New Zealand the population of Havelock North was exposed to camphylobacter in their bore water supply which had been contaminated by pond water from a nearby sheep farm (Wilson, 2017).

Another problem in drinking supplies is heavy metals such as arsenic, manganese, iron, cadmium, boron, lead and mercury. Most of these contaminants can induce cancer and the other associated affects have been significant as well (Chowdhury

et al., 2016). In the Waikato region 33% of bore water contains high arsenic

concentrations greater than the drinking water standard. Elevated levels of iron and nitrate are the most common ground water contaminants in the region. Most

(14)

frequently iron and manganese co – exist in bore water (Waikato Regional Council, n.d).

Scientific research on water resource protection, water treatment, purification and water safety is becoming more important as scarcity of clean drinking water increases (Blatter & Ingram, 2001). Promising water purification and disinfection innovations include:

 Composite materials and nano particles developed for pathogen removal (Quang et al., 2013; Tartanson et al., 2014)

 Solar water disinfection (SODIS) (Hindiyeh & Ali, 2010).

 Photo- fenton method which using a mixture of ferrous ions and hydrogen peroxide, called Fenton’s reagent, to oxidise organic water contamination (Ortega-Gómez et al., 2012).

 Perforated Electrode Flow Through (PEFT) cell for chlorine production and disinfection (Nath & Langdon, 2013).

Compared to traditional disinfection methods such as chlorination, ozonation, and UV that have been used for decades, these novel techniques have a number of advantages (Ortega-Gómez et al., 2012):

 Less or no storage facilities needed  Less hazardous by-product generation  No transport of chemicals or leakages  Low cost

Therefore further developing these products will add in the evolution of water technology.

1.2 Research objectives

At the University of Waikato, the PEFT cell was developed that consisted of two perforated electrode plates spaced about 50 micrometers apart, contained within a chamber. An electric current between the plates electrolyzed a brine solution producing chlorine for disinfection. This system was only able to be operated in series. A new system was designed that allowed the system to be operated in parallel enabling greater throughput.

(15)

The aim of the research is to:

 Optimize the chlorine production of the new PEFT cell

 Assess optimum current for the maximum chlorine production

 Assess optimum operating voltage for the maximum chlorine production  Assess optimum salt concentration of brine water (NaCl solution)

 Assess optimum flow rate of the brine water ( NaCl solution)  Assess disinfection properties on solutions containing E – coli

 Ability to remove iron and manganese dissolved in water by combining the PEFT cell with a DMI65 column will be assessed as the secondary objective.

1.3 Thesis outline

In Chapter Two a literature review is presented on water, water pollution, current treatments in water purification, evaluation of electro-chlorination in water disinfection and the use of PEFT as productive, low cost and in-situ chlorine generator. Furthermore, the chemical and physical behavior of the traditional treatments is presented.

Methodology and materials in this research are presented in Chapter 3.

In Chapter 4, results obtained from the study are presented and discussed.

(16)

2 Literature Review

2.1 Introduction

Purpose of this chapter is to guide the way enhancing performance of the PEFT cell and facilitate a background study to have a better understanding on the water, water contaminates, water quality standards, water treating methods and function of novel PEFT cell in water treatments. Study is relevant to New Zealand as to support the practical works carried out based on New Zealand water sources and standards.

2.2 Water

Pure water is colorless, odorless and tasteless and commonly found in liquid form that has number of unique properties. The chemical and physical nature of water makes it an un-replaceable essential for the existence of life (Shakhashiri, 2011).

Chemically water can be defined as a molecule formed by two hydrogen atoms and one oxygen atom. Group 6 ‘O’ atom has two unpaired electrons and group 1 ‘H’ atom has one unpaired electron; thus one ‘O’ atom shares it’s two unpaired electrons with two ‘H’ atoms each donating one unpaired electron to form a covalent bond (Evangelou, 1998). Unshared electrons in ‘O’ exert repulsive forces against each other and shared electrons exert less repulsive forces compared to unshared ones. This phenomenon makes oxygen skewed and the water molecule polar. The oxygen atom is slightly negatively charged and each hydrogen atom is slightly positively charged (Figure 2.1: Left). Polarity of the water molecule leads it to make weak hydrogen bonds with other polar molecules (Figure 2.1: Right) and it is the reason water is considered “the universal solvent”. Hydration is specific property water molecules demonstrate due to their polarity (Evangelou, 1998; Vaclavik, 2014).

(17)

Figure 2.1 Left: Polar water molecule, Right: Hydrogen bonds between water molecules (commons, 2013; Lodish, 2008)

2.3 Water sources

Water divides into two categories: saline or sea water and fresh water. Saline

contains 35,000 mg.l-1 oftotal dissolved solid, mainly due to sodium chloride and

fresh water is less than 500 mg.l-1 of total dissolved solid. Saline and fresh water

sources and their contribution to the global water availability are shown in Table 2.1.

Table 2-1 Water sources and their contribution to global water availability (Agnew, 2011)

Oceans Snow and ice Ground water Atmospheric Lake and rivers Soil moisture Saline Fresh water Fresh water Fresh water Fresh water Fresh water 1.350,000,000 km3 27,500,000 km3 8,200,000 km3 40,000 km3 207,000 km3 70,000 km3 97.37% 1.98% 0.59% 0.033% 0.015% 0.005%

Water sources can also be categorized into surface waters and ground waters.

2.3.1 Surface waters

Surface waters refer to any source of water body that flowing or appear on the earth surface. Rivers, lakes and reservoirs are surface waters generated from different sources such as surface run off, direct rain fall into a water body or inter flow (Gray, 1999).

(18)

Most of the time heavy rain falls that cannot totally be absorbed by the vegetation and soil; create water steams such as rivers. These surface water run-offs are nurtured by the underground waters that penetrate through the soil as springs (Matthews, 1985).

Since ground waters also contribute in generating surface water, it indirectly affects the quality of the surface waters. A reasonable amount of dissolved solid comprised of soil, volcanic materials, bacteria, fungi and chemicals originate from ground water. Chemical discharges from industrial production accumulated in the atmosphere are brought back to surface water with rain fall (Gray, 1999).

Among various water sources, rivers themselves contain 0.0002% of water on Earth and 0.46% of the surface fresh water. River water conditions in New Zealand are identified as fairly good or very good compared to Europe, North America and Asia, but it has been declining over past 25 years by point-source pollution (wastewater discharge from industries and agriculture) and diffuse pollution from land use (Davies-Colley, 2013). New Zealand has a large number of lakes as well, but improper land use and submerged plant growth in these lakes has had negative impacts on water quality that restricts their use as a drinking water source (Verburg et al., 2010).

Using river water for industrial, commercial and household water supply is common in New Zealand. The Waikato River is the longest river in New Zealand (425 km) which takes water from several other water bodies such as the Waipa River, Lake Taupo and Lake Karapiro (Kingston Reynolds et al., 1975).

2.3.2 Ground waters

Groundwater is one important portion of water in the hydrological cycle. Water located in the Earth’s crust are simply identified as ground water, and originate from surface water bodies (Todd, 2004).

(19)

Figure 2.2 Global hydrological system (Todd, 2004)

Groundwater/sub-surface water is 98.97% of total fresh water and surface water and atmospheric water account for the remaining 0.87% and 0.16% respectively (Young, 2007). Groundwater reservoirs are interconnected by groundwater streams which are not rapid moving water streams such as surface waters. These groundwater storages are different according to their geological formation. The most frequently used underwater source, aquifers, are referred to as a saturated permeable reservoir with sufficient water quantities for springs and wells. These are water storages that have the ability to transmit water through the covering rock shells (unconfined storages). There are a few other confined beds that may or may not contain water. Aquiclude is saturated rock but with insufficient quantities of water for wells and no permeable cover. Aquifuge is a bed with impermeable layer of rocks without transmittable water in it. Aquitard is a water source that has poor permeable materials and impedes the groundwater movement (Todd, 2004). Visible surface water sources and aquifers are related to each other and share water in both directions. Mobile water seeps in between the surface and ground water systems depending on the area of contact (Margat, 2013). When

(20)

water migrate either direction, it carries water soluble contaminants from one existing source to the other.

2.4 Water contaminants

The basic structure of environmental systems is disrupted by human activities and pollutants such as sewage, industrial byproducts, agricultural and radioactive materials. It is noted that natural processes also release harmful substances that can also cause serious impact on the environment. Water contamination is a crucial problem worldwide, but the water pollution in New Zealand is much less compared to Europe (which is highly industrialised) or Asia (which is highly populated) (Connell, 1993).

Chemical, physical or biological changes are caused by water pollution. Parameters such as suspended solids, turbidity, odour, nutrient levels, pH, heavy metals, non-metallic toxin levels, persistent organics and pesticides, and biological factors (BOD value, COD value) define the level of contamination (Palaniappan et al., 2010). As groundwater and surface water sources are connected and exchange contaminants, the safety of the drinking water extracted by surface water or ground water source is affected by what has been discharged, e.g. micro-organisms, chemicals and even by disinfection by products (U.S. Environmental Protection Agency, 2013). According to a survey done in London, incidents of public health threatening water contaminations have been categorized and found the most frequent incidents are due to poor drinking water quality, chemical contamination, microbiological contamination and poor weather conditions (International Conference on Water Contamination, 2011).

High concentrations of water contaminants cause several problems to the quality of the water as well as to water treatment plant equipments and pipelines. Chloride from the mine water induces corrosion in pipelines and many other salts such as sulphates and carbonates result scaling or blockage (Scaling is chemical decomposition by crystallization or precipitation due to dissolved salt concentrations exceed saturation limit) (Stephenson, 1988).

(21)

Occurrence of health effecting contaminates in drinking water may be varied due to the source. Qualification and quantification analysis include observations in tap water, distribution systems, treated water in water treatment plants, source water, water sheds and aquifers, and historical and chemical production data (Contaminants, 1900).

Table 2-2 Drinking water Contaminants (Contaminants, 1900; Ministry of Health, 2007)

Inorganic contaminants

(including heavy metals)

Organic contaminants Biological contaminants

Barium Beryllium Cadmium Chromium Cyanide Fluoride Mercury Nitrite Selenium Calcium Chloride Ion Arsenic

Silica (organic and

inorganic) Lead Manganese Benzene Benzoic acid Carbofuran Carbon tetrachloride Ascorbic acid Citric acid Ethanol Folic acid Glycerin Glycine

Viruses – Hepatitis A, flu virus, polio Bacteria – Campylobacter, Salmonella, Shigella , E- coli Protozoa – Cryptosporidium , Giardia Cyanobacteria– Cylindrospermopsin

Issues can be caused by some of the chemical substances contaminated in to water and their maximum levels are listed below (Chhatwal, 1996):

Arsenic (As) – since arsenic is present in tobacco and other food sources, the level of Arsenic in drinking water must not exceed 0.01ppm.

Cadmium (Cd) – electroplating activities and zinc galvanizing causes elevated levels of cadmium in water. Concentrations up to 0.01 ppm are acceptable.

(22)

Chloride (Cl-) – higher levels of chloride make water taste salty. Maximum acceptable level of chloride is 250 ppm.

Chromium (Cr) – industrial pollution (plating/ tannery activities) add chromium

ions with different valences. Hexavalent chromium (Cr+6) is the most toxic form

and it should not exceed 0.05 ppm.

Cyanide – the level of cyanide in water should be less than 0.01 ppm.

Iron (Fe) – iron in the water is common due to industrial operations as well as from the soil. It can cause health effects when consumed and damage to laundry and plumbing systems. The upper limit for iron is 0.3 ppm.

Lead – Serious health hazards are caused by lead replacing some of the metal ions in enzymes and deactivating them. The limit set for lead in water is 0.05 ppm. Manganese – the upper limit is 0.05 ppm.

Other than the chemical contamination, one of the most concerning contamination of water is biological contamination (Oliveira et al., 2013). Many studies on drinking water related diseases show pathogenic organisms such as viruses, bacteria, fungi, protozoa have been the cause. According to a research carried out in by EPA collaboration with Centers for Disease Control and Prevention (CDC) in the U.S., the most infectious pathogens were Giardia, Campylobacter, Cryptosporidium, Salmonella, zoonotic agents and E- coli bacteria. Public health issues including deaths and serious illnesses have been reported over the years. Outbreaks of these pathogens are associated with untreated or inadequately disinfected ground water, contamination of distribution systems where there are cross-connections, breaks and repairs, deficient storage tanks and unprotected reservoirs (Staff, 2005b). Statistical investigations by the EPA has identified even though most of the surface water goes through a disinfection process prior to the consumption, their quality often does not match the required standards. One other reason for the increasing number of pathogenic infections is most of the virus and bacteria show some resistance to physico-chemical disinfection treatments, because they have adapted to those treatments (Gleeson, 2002).

Water related microorganisms can be divided into water based and water borne pathogens. Water based pathogens need water to complete some of the stages of their lifecycle, but the waterborne pathogens spend their whole life in the water and are transmitted via the fecal-oral route. Identification of water borne

(23)

pathogens is not easy. For the water monitoring procedures and other statistical evaluations quantitative data collection (bacterial counts etc.) is necessary. A widely used indicator organism is Escherichia-coli bacteria (Baker & Bovard, 1996). In the early stages of water microbiology, pathogen microbiologists made a list of criteria as an attempt to find an indicator pathogen. The main concern was the concentration or number of indicator microorganisms should be related to the extent of water contamination. Use of cholera vibrio as an indicator was had difficulties in isolating them in the water samples. In 1885, Escherich was able to identify a group of bacteria called coliforms as indicator bacteria which were easy to isolate. So, coliforms were quickly recognized as more accurate water quality indicator, and further evaluation of bacteriological techniques were able to detect even small numbers of coliform bacteria (Gleeson, 2002). Even now, the coliform index is still widely used to measure water quality. In this study, E-coli bacteria are used as the indicator to measure the disinfection power of the PEFT cell.

Coliforms are gram- negative, anaerobic, rod shaped bacteria where Escherichia-coli is the most common type of Escherichia-coliform bacteria found. E-Escherichia-coli bacteria containing samples grow in an agar medium made of lactose-peptone-eosin-methyl blue (EMB). After introducing a sample on to the medium it is incubated for 24-48 hours at about 37°C. E-coli bacteria grow as red colour colonies that can be counted using a microscope (Torres, 2010). Comparing E-coli counting with the E-coli standard index, conclusions on the water quality can be made.

Figure 2.3 Scanning electron micrograph of Escherichia coli bacteria (Mundasad, 2011)

(24)

With the increasing industrialization and population, water contamination becomes more frequent and more complex. There is an emergence of research programs regarding expanding technology of water purification (Guidotti, 2009). The Department of Health and Human Services of United States has appointed environmental health policy committee which has a subcommittee on drinking water and health, and its role is to identify and take action where immediate attention is required. As observed by the committee more research is needed in areas of relationship between contaminants and adverse health effects, developing methodologies and models to understand the situation, developing laboratory techniques to measure the hazard and expanding the knowledge about waterborne health hazard in order to prevent them. The committee is assisting EPA (Environmental Protection Agency, US) in setting priorities for future drinking water contaminants and introducing new scheme to prioritize all contaminants based on their toxicity to human health/eco-systems, persistence, bioaccumulation and mass of the contaminant in the water streams/water sources. Furthermore, creating a future drinking water candidate list (CCL) has being considered over years with expertise knowledge that can predict potential contaminants and the way they behave in the water (National Research Council, 1999).

Ministry of Health, New Zealand, made a report on public health issues concerning drinking water. Department of Internal Affairs also collaborated in the project by reviewing where need funding and delivery of water and waste-water services was needed. According to the report public water supplies are in risk of contamination by chemical and biological substances because of inappropriate use

of land, industry waste and farm waste disposal(Ministry of Health, 1994). While

the Ministry of Health focuses on improving legislative and administrative support, the Department of Internal Affairs monitors and funds local authorities to overcome the issues.

2.5 Water standards

Water quality is influenced by number of key determinants such as geological location, climatic nature, hydrologic and geomorphic processes that associate the virgin water sources and human interaction (Baillie & Neary, 2015). Land uses for farming, forestry, mining and quarrying and waste disposal have a great impact on

(25)

New Zealand’s water (Reid et al., 2012). World Health Organization (WHO) encourages every nation to follow better treatments and strategies to maintain the water standards to minimize or eliminate significant hazards during human consumption (Oliveira et al., 2013). General water quality requirements for household water are shown in table 2.3.

Table 2-3 General quality requirements for household water (Health, 2013)

Household use Quality requirement

Drinking Biologically and chemically safe

Cooking and food preparation Biologically and chemically safe

Bathing/showering Biologically safe

Toilet flushing Not discoloured or stain causing

Cloth washing Not discoloured or stain causing

Both the water and waste water treatment processes follow water quality guidance in scientific and engineering approaches. After quantification analysis based on data collected and qualification analysis regarding chemical, microbiological, ecological and engineering aspect, standards are set to monitor the quality of water (Waite, 1984). The purpose of the setting drinking water parameters is to ensure the prevention of poisoning and long term health effects (Safe Drinking Water, 1976) .

In New Zealand, the main legislation for protecting water sources and drinking water standards include (New Zealand. Drinking-Water Regulatory & New Zealand. Ministry of, 1995):

Resource Management Act 1991

This gives regional councils responsibility to control the land use to protect the source water quality, control taking, using, damming and diversion of source water, and control discharges to the source water.

Water Supplies and Protection Regulations 1961

This covers protection of water distributed by the distribution system, i.e. every reservoir should have appropriate cover to protect stored water from

(26)

contamination, and newly constructed reservoirs and distribution systems should be disinfected prior to the use.

Health Act 1956

This act was to ensure quality of the water supplied to the community, protect water courses, reduce the impact of discharges from treatment plants and protect individual house hold water quality.

Local Government Act 1974

This act supports the Health Act 1956 in the areas of water quality.

Under these legislations and acts there are a number of frameworks to establish drinking water quality. National Environmental Standards for raw drinking water sources prepared by Ministry for the Environment in 2004 propose a water quality grading system for the source waters. The Ministry of Health uses a ‘Multi-barrier approach’ in drinking water management to minimize the risk of chemical and microbiological contamination (Ministry for the Environment, 2004). A multi-barrier approach is a collection of several procedures, processes and tools that work together to reduce or eliminate contamination of drinking water from source to tap.

The grading system considers two factors, individual grade for identified contaminants and overall grade to check the suitability of raw water source. Individual grades for the contaminants are given based on catchment risk category and water quality category. (Ministry for the Environment, 2004)

Water quality regarding the contamination level for individual contaminants and the catchment is represented by a colour scale (Table 2.4, 2.5).

(27)

Table 2-4 Colour scale uses for the individual contaminant grading (Ministry for the Environment, 2004)

Grade Suitability

description

Interpretation

Green Very good suitability No treatment required

Yellow Good suitability Reliance on treatment to reduce low levels of

contaminant to acceptable levels

Orange Fair suitability Reliance on treatment to reduce moderate

levels of contaminant to acceptable levels

Red Poor suitability Reliance on treatment to reduce high levels of

contaminant to acceptable levels

Black Very poor suitability Heavy reliance on treatment to reduce

contaminant to acceptable levels

Table 2-5 Overall grade of source water and grade interpretation (Ministry for the Environment, 2004)

Grade Level of Suitability Interpretation

Green Very good suitability No treatment needs to make the water safe for

drinking

Yellow Good suitability Reliance on treatment to remove low levels of

microbes to make the water safe; or chemical or cyanobacteria present

Orange Fair suitability Reliance on treatment to remove moderate

levels of microbes to make water safe

Red Poor suitability Reliance on treatment to remove high levels of

microbes, chemicals or toxins to make water safe

Black Very poor suitability Heavy reliance on treatment to remove high

levels of microbes to make water safe

Grading procedure of the drinking water is further broadened and updated by the Ministry of Health (Ministry of Health, 2001) to achieve international standards of water quality for supply (Table 2.6 and 2.7). Not only source water quality determines suitability of consumption, but also treatment procedure and

(28)

distribution system. Therefore the Ministry of Health introduced a merit and demerit point grading system which was a hybrid protocol of existing grading systems at that time and the output of the Public Health Risk Management Plan (PHRMP).

Table 2-6 Keys use to grade source, treatment and distribution (Ministry of Health, 1995, 2001)

Grade Description

A1 Complete satisfactory, negligible level of risk, demonstrably

high quality

A Complete satisfactory, very low level of risk

B Satisfactory , low level of risk

C Marginal, moderate level of risk, may be acceptable for small

communities

D Unsatisfactory, high level of risk

E Complete unsatisfactory, very high level of risk

Table 2-7 Total points for the grading (Ministry of Health, 2001)

Grade A1 A B C D E

Points >90 80-89 70-79 50-69 40-49 < 40

Total points given for a source water/treated water or distributed water is sum of merit points and demerit points (Table 2.8 and 2.9).

(29)

Table 2-8 Award merit points for source/ treatment and distribustion criteria (Ministry of Health, 2001)

Compliance Merit points for

source/treatment

Merit points for distribution

E-coli compliance 49 60

P2 compliance 5 5

Protozoan compliance (only for source water/ treatment)

Corrosion compliance (only for

distribution)

15 5

Disinfection with residual 10 10

Aesthetic guideline value 5 10

ISO 14001/9002 16 10

P2 compliance – contaminated material getting in to water source

Demerit points are based on risk criteria such as not being able to draw enough water, water contamination, non-secure surface water or ground water, algicide, destratification, pre-oxidation, processes of coagulation, flocculation and clarification, aesthetics and fluoridation which are given deduction points ranging from 0 to 5 (Ministry of Health, 2001).

Drinking water standards for the New Zealand (DWSNZ) covers all areas of drinking water quality requirements that have been set for water delivery. DWSNZ specify the Maximum Acceptable Value (MAV) for each water contaminant (Table 2.9 and Table 2.10). MAV is concentration of a determinant in drinking water that is identified as no significant health risk to the consumer over the lifetime of consumption of that water (Ministry of Health, 2005).

Table 2-9 Maximum acceptable values for microbial determinants (Ministry of Health, 2008)

Micro-organism Maximum Acceptable Value

Escherichia coli Less than one in 100 ml sample

Viruses No values set due to lack of reliable data

Pathogenic protozoa Less than one infectious oocyst per 100 ml

(30)

Table 2-10 Guideline values (GV) for aesthetic determinants (Ministry of Health, 2008)

Determinant GV Unit Comment

Aluminum 0.1 mg/L Above this depositions and

discolouration could happen

Ammonia 1.5 mg/L Odor threshold in alkaline

conditions

Calcium Hardness is checked

Chlorine 0.6- 1.0 mg/L Taste and odor threshold

Chloride 250 mg/L Taste and corrosion

Total hardness (Ca +Mg)

200 mg/L Deposition, scum formation and

corrosion

Iron 0.2 mg/L Staining

Manganese 0.04 mg/L Staining

Sodium 200 mg/L Taste threshold

Sulphate 250 mg/L Taste threshold

Zinc 1.5 mg/L Taste threshold

2.6 Treating water

Water treatment is defined as the process of achieving the required water quality and standard by various treatment steps. Boiling water over fire, dipping heating rods into water and filtering water through sand and gravel filters have been in use since 4000 B.C. In 1804 the first municipal water treatment plant was installed in Paisley, Scotland. In 1829 slow sand filters being used to filter water. In 1835 operators started adding small amounts of chorine to disinfect water as recommended by Dr. Robley Dunlingsen. In 1856 Thomas Hawksley introduced a pressurized water system to prevent contamination. In 1881 laboratory tests identified chlorine was able to destroy bacteria. In 1892 Theobald Smith detected E-coli bacteria in water as a result of sewage contamination to water. In 1906 ozone was used for disinfection for the first time. In 1914 the fermentation tube method introduced by Theobald Smith came to practice in U.S Public Health Service to set biological standards of water and by the year 1941, 85% of the water supplied in USA had been chlorinated (Crittenden, 2012).

(31)

Factors affecting the selection of water treatment processes include (Staff, 2009):  Source of water (ground water or surface water)

 Required treated water quality  Capital and operating costs  Plant installation

 By-products, residual disposal

 Applicability

All the water treatment processes contain a set of basic unit processes that each removes a targeted contaminant based on physical, chemical or biological theory. In other words, a treatment program is an integrated train of unit processes that remove or reduce undesirable constituents from the water reach the required drinking water standards (Schutte, 2006). Basic unit processes are listed in Table 2.11.

(32)

Table 2-11 Unit processes and applications (Schutte, 2006)

Unit process Description and application

Screening Screens are used at the intake gate or in the sump well

ahead of pumps. Remove debris in the raw water

Aeration Supply air in to the tanks. It oxidizes taste and

odor-causing chemicals and oxidizes iron and manganese.

Mixing Mechanical mixers use to mix the chemicals added in to

the water

Coagulation Add coagulants in to water to destabilize colloidal

particles and promote making flocs

Flocculation Facilitate aggregation of small floc to larger ones

Sedimentation Allow sediment larger flocs or suspended particles in to

the bottom of the sedimentation tank. And separates water layer

Sand filtration Further removal of suspended particles or flocs in the

water by passing water through multi-size sand/gravel filters

Activated carbon

adsorption

Remove many small particles by adsorbing them in to the porous surface of activated carbon. It also removes many metals. It can be either powdered activated carbon (PAC) or granular activated carbon (GAC)

Ion exchange Cation and anion resins are used to remove selected ions

already have dissolved in the water. Resin beds are replaced when they reach maximum exchange level

Disinfection Disinfection is important in drinking water treatments in

order to kill all the disease causing organisms. Chlorination is the most popular disinfection method. But alternative disinfection methods such as ultraviolet radiation, ozone and chlorine dioxide are used either combined with chlorine or not

2.6.1 Screening

Screening (e.g. bar screens, fine screens, drum screens, and micro-screens) is a preliminary treatment step almost every water treatment process uses (water

(33)

treatment and waste water treatment) to remove large sized solid contaminants (Hendricks, 2006).

2.6.2 Sedimentation

Suspended particles that cannot be separated by screening can be removed by allowing them to settle in sedimentation tanks. Settling velocity depends on particle size, shape, charge and specific gravity (Julien, 2010).

2.6.3 Coagulation

Particles which do not settle out can include humic materials such as tannins, lignins, phenolics, hydrocarbons, amino acids, trace metals, colloidal solids, bacteria, viruses, color causing particles or fine silts (Berger, 1987; Staff, 2009). These generally have a negative charge repelling each other and remain dispersed by Brownian motion (Prakash, 2014). These are treated by adding a coagulant such as alum, an iron salt or polymeric material that promotes charge neutralization and causes the particles to form small flocs (figure 2.4) (Howe, 2012; Racar et al., 2017). Polymeric materials can be polyelectrolytes which have the ability to charge neutralize and make agglomerates or non-ionic polymers that bridge between colloidal particles to form larger agglomerates (figure 2.5) (Gregory, 2004).

(34)

Figure 2.5 Cationic polyelectrolyte and Anionic polyelectrolyte

2.6.4 Filtration

Filtration is a physical-chemical process which involves passing water through a filter media to remove undesirable dissolved particles (Todaro, 2014). This can be rapid filtration, slow sand filtration, membrane filtration or a combination (Staff, 2010).

2.6.4.1 Rapid gravity filtration

Rapid gravity filters are packed bed of granular media of specific material that remove suspended substances by physicochemical mechanism (Han et al., 2009). This has been the most widely used last step to remove suspended particulates in water treatment process by municipal water supply systems. Turbidity, suspended particles, water-born pathogen, and some trace metals (e.g. iron and manganese removal is possible during rapid gravity filtration (Upton et al., 2017) (Tatari et

al., 2016).

2.6.4.2 Slow sand filtration

Slow sand filtration uses biological activity from planktons, diatomas, protozoa and bacteria on the filter surface (called a schmutzdecke) to remove pathogenic microorganisms and organic pollutants (Seeger et al., 2016). Filter systems consists of a basin with relatively fine sand, underline outlet pipe and water inlet above the filter bed. The water outlet is surrounded by supportive gravel about 0.4 m – 0.6 m deep and on top of it is filter sand which typically is 0.8 m to 1.2 m in depth. Slow sand filters have very low filtration rates of between 0.1 to 0.3 m/hour (Logsdon, 2008). Quartz sand used in slow sand filters is usually

(35)

negatively charged and has great bonding capability iron, manganese, aluminum and other metals (Huisman, 1974).

2.6.4.3 Membrane filtration

A membrane filtration process uses permeable membranes which permit water to flow through while resisting the passage of other suspended solids. Membrane filtration includes reverse osmosis (RO), nano-filtration (NF), micro-filtration (MF) and ultra-filtration (UF). MF and UF typically have pore sizes between 0.1 – 0.2 μm and 0.01 – 0.05 μm respectively while NF has pore sizes around 0.001μm. (Gupta, 2012). Reverse osmosis will allow water to pass while rejecting salts, while separation using UF and MF will reject protein sized molecules while allowing passage of salts and water (figure 2.6).

Figure 2.6 Filtration spectrum of MF, UF and NF (YAMIT Filtration and Water Treatement, n.d.)

2.6.5 Adsorption

Adsorption uses an absorbent which consists of a highly porous material such as activated carbon to absorb trace taste, odour, organic and metal compounds from water (Marsh, 2006)(Worch, 2012) through hydrophobic, electrostatic, and Van der waals interactions (Cheremisinoff, 2001). Physical adsorption can be increased by increasing porosity and chemical adsorption by increasing functional groups containing oxygen compounds such as acidic surface oxides, and carboxylic, phenolic and carbonyl groups (Cecen, 2011). Granular activated

(36)

carbon is popular in water and drinking water treatment processes (Bahadori, 2013; Committee, 2011).

2.6.6 Ion exchange

Another form of adsorption is ion-exchange which uses a polymer resin to exchange similarly charged ions with ions in water (Slater, 1991). In practical cation and anion exchangers are placed in series for removal of salts (Paterson, 1970) and trace metals in water (Walton, 1990) such as manganese, zinc, barium, cadmium, chromium, lead, silver and mercury (Muraviev, 1999). One of the major drawbacks of ion exchange is it is not possible to exchange all the counter– ions due to several issues such as adsorption capacity and the need to regenerate the resin periodically to recover ion exchange capacity (Bolto, 1987).

2.6.7 Disinfection

Disinfection is destruction or deactivation of possible infectious species. Prevalent disinfection methods use in the drinking water purification/treatment process is chlorination, ultraviolet radiation and ozone (Kuo & Smith, 1996). More detailed review on individual disinfection modes will be delivered under ‘2.7 Disinfection’ section.

2.7 Disinfection

Poorly managed or poorly treated water utilities can result in microbiological waterborne diseases. Vulnerability depends on the potential of the water source to be microbiologically contaminated, treatment efficiency, treated water distribution system quality and general management (Joerin et al., 2010; Nokes, 2004) Other than preventing contamination of source water with pathogens, using disinfection methods is the general strategy in water purification technology (Voeller, 2014).

A disinfectant is a chemical or physical agent that is capable of destroying diseases causing bacteria, fungi, viruses and protozoa but not be successful in inactivating bacterial spores. A bactericide, fungicide or virucide will destroy a particular bacteria, fungi or viruses respectively while a germicide destroys range

(37)

of pathogenic organisms without focusing on particular species. Disinfection differs from sterilization which demolishes all organisms (Das, 2000).

2.7.1 Physical disinfection

Physical disinfection utilizes heat, radiation and filtration to deactivate microbial communities. Heat is the most widely used primary physical disinfection method which transfers thermal energy from one system to another due to temperature difference by conduction, convention or radiation. The mode of heat transfer can be wet or dry. Wet heat is considered as most effective form of heat as liquid or gaseous (steam) phase of water act as the disinfection agent. Dry heat is less effective under 140°C and usage is limited due to it. Radiation is emission of energy of unstable atoms as particles or electro-magnetic waves. Energy transmitted in the form of rays are, X-rays, ultra violet (UV) radiation and infra-red (IR) (McDonnell, 2007).

2.7.2 Chemical disinfection

Historically chemical disinfection was used as an additional operation parallel to physical disinfection until the early 19’s; after which chemical disinfectants were more common (Buchanan, 2011). Most of the disinfection methods used nowadays in house hold and large scale water treatment plants are chemical disinfection methods. There are four widely used chemical disinfectants: free chlorine, hypochlorite, chloromines, chlorine dioxide and ozone (Twort, 2000). Chlorine has been the dominant and important water disinfection method used all over the world as it produces a residual that continuously delivers disinfection during distribution until consumption (Percival, 2013). These disinfectants destroy or damage the cell wall of microorganisms or get into the cell and inhibit enzyme activity of the microorganism. Factors effecting disinfection are contact time, concentration and type of disinfectant, intensity and nature of physical agent, temperature, number of microorganisms, type of microorganisms and water conditions (Das, 2000). Degree of removal or percentage removal of microorganism is used to define the disinfection yield. Chick’s law describes the relationship of the rate of inactivation microorganism.

(38)

dN/ dt = kCN Equation 1

Where N is the number of microorganisms, t is time, k is a rate constant which depends on the disinfectant, type of microorganisms and water quality, and C is concentration of the disinfectant (Disinfection, 2013).

2.7.3 Chlorination

Chlorine was discovered in 1774 by Swedish chemist Carl W. Scheele. Application of chlorine as a disinfectant started in 1908 for the Boonton water supply with filtration processes (McGuire, 2012). Chlorination has been used as the predominant disinfection method for 70 years in United States and it contributes 95% of disinfection of portable water. Chlorine is reactive against most of the pathogens (National Research Council, 1986) and widely used as because it is readily available as gas, liquid or powder, cheap, easy to apply, has high solubility in water, provides residual disinfection while distributing (Race, 2011; Tebbutt, 1997).

Chlorine dissolves in water forming mixture of hypochlorous and hydrochloric acids and the reaction is pH sensitive.

Cl2 + H2O HOCl + HCl Equation 2

Chlorine dissolution mechanism shows following equilibrium,

Cl2 + H2O HOCl + H+ + Cl- Equation 3

HOCl + H2O H+ + OCl- Equation 4

Hypochlorite ions (OCl-) and hypochlorous acid (HOCl) together are termed as

“free chlorine”. Hypochlorous acid is more affective in deactivating

microorganisms than OCl- ions. Therefore the pH condition should be controlled

in favor of making more hypochlorous acids, i.e. pH 6 – 8. The concentration of HOCl is significantly reduced by organic matter and ammonia present in the water (Gomez-Lopez, 2012; Li & Zhang, 2012; Race, 2011).

(39)

Chlorine gas is greenish-yellow in color, reacts violently with many substances, and therefore is impossible to find pure chlorine gas in nature. Chlorine gas is manufactured by electrolysis methods from sodium chloride brine, and stored as a compressed liquid. The acids that form when it reacts with water are corrosive to metallic treatment plant equipment (Staff, 2005a).

Chlorine is also useful in metals removal from water supplies. Both free chlorine and combined chlorine react with ferrous and manganese ions to oxidize them.

2Fe 2+ + Cl2 + 6H2O 2Fe(OH)3 + 2Cl- + 6H+ Equation 5

Mn2+ + Cl2 + 2H2O MnO2 + 4H+ + 2Cl- Equation 6

Even ferrous bicarbonate (FeHCO3) is oxidized to ferric hydroxide. Free elemental chlorine is more effective than the combined chlorine in oxidizing iron present in complex organic combinations.

Chlorine reaction with manganese ions gives manganese dioxide which is a solid but appears in colloidal form rather than particulate forms. Therefore the conventional filter media used to remove the colloidal form of manganese dioxide, is recommended to operate with excess chlorine in it to ensure oxidation of any adsorbed Mn deposits. Oxidation of manganese ions by free chlorine requires a longer contact time and the deposition of oxidized iron and manganese in plumbing systems are the major issues (White et al., 2010).

Chlorination can also be achieved by adding chlorine compounds such as sodium hypochlorite, chloromines and chlorine dioxide (Park & Allaby, 2013). Chlorine dioxide (ClO2) is stronger oxidant than chlorine and other chlorine compounds, is active over a wide pH range, but its use is limited in water treatment due to its complexity, risky nature of generation and high cost. Chlorine dioxide can also results in disinfection by-products (DBP) such as trihalomethane (THM) precursors (Solsona, 2003). Chloromines are a combination of chlorine and ammonia in water media to form monochloroamine at pH 8.3(Texas Commission on Environmental Quality, 2015):

(40)

HOCl + NH3 NH2Cl + H2O

Chloromination produces residual disinfection, acts as a biocide in the distribution system, does not create THM and formation of DBP is negligible. However, addition of ammonia contributes to nitrification in the waterways which can enhance pathogenic community growth and at the same time reduce residual chloromine amount (Staff, 2005a).

One major drawback of most of the chlorine disinfection methods is on-site generation requirement. It demands a large capital cost for storage tanks, chemical feed pumps, buildings to set up equipment, electrical and mechanical power. Structural modifications and maintenance over the time need additional money for physical apparatus and professional fee. It may require substitution mini plant in water treatment plant in case of breakdown or situations such as shut down for maintenance if the plant is covering large area of water supply. As process has to depend on the external chemical supplement, planning and monitoring deliveries and onsite chemical stocks is proposed. Chemical handling requires special training and supervision which is more labor intensive (Staff, 2014).

2.7.4 Ozonation

Ozone (O3) is tri atomic structure of oxygen which forms according to the reaction of O2 with another free radical oxygen. Central oxygen atom is attached to other two oxygen atoms in a particular angel of 116° 49´. All three oxygen atoms in ozone contain two unpaired electrons in valence cell. Since ozone molecule appears with two resonance structures it shows electrophilic and nucleophilic behaviors due to absence of one electron of each terminal oxygen at different stages (figure 2.7).

(41)

This structural nature of ozone makes it a vigorously reactive molecule. Formation of ozone (O3) needs diatomic oxygen (O2) to break down in to free radicals and those extremely reactive free radicals to react with other diatomic oxygen. Splitting of diatomic oxygen requires pronounced amount of energy usually acquires from UV radiation (188 nm wave length) (Donnell et al., 2012).

O2 + UV radiation O* + O* Equation 7

O2 + O* O3 Equation 8

Alternative reaction mechanism for ozone production is NO2 photolysis which also produces a free radical oxygen (Mathieson, 2010).

NO2 + UV radiation NO + O* Equation 9

O2 + O* O3 Equation 10

Mechanism of ozonation explains the reason it to be more effective oxidant. Both direct and indirect chemical reactions occur in water simultaneously makes ozone way better than other oxidants; but reaction conditions such as pH of water, dissolved organic matter level and alkalinity impact on the reactivity. Indirect

reaction initiates by OH- free radicals in water which are very unstable and

looking for electrons, to be stable.

O3 + OH- O2- + HO2- Equation 11

HO2- O2- + H+ Equation 12

All of these reactive species undergo radical reactions and form compounds after reacting with organic and inorganic substances in water. Ozone acts as an electro-philic agent with aromatic compounds and nucleo-electro-philic agent with carbonyl compounds during direct reactions (Donnell et al., 2012), and will also attack alkanes and cycloalkanes which is helpful in removing large organic compounds (Knipe, 2012). Ozone will attack cell membrane glycol-proteins, glycol-lipids and enzymes. After damaging cell membrane it will attack protein and DNA inside

(42)

(Donnell et al., 2012). In addition, ozone is useful in oxidizing metals in water. Ozone will not produce DBPs, but it does not provide residual disinfection. It can

also produce bromate (BrO3-) which is a carcinogenic substance from bromide

(Br-) containing water (Gottschalk et al., 2010) which has limited use of ozone as

a disinfectant (Loeb et al., 2012).

Practical methods of ozone generation is allowing an electrical discharge to happen between high electrically charged conductors separated by an air gap. Techniques such as corona discharge, surface discharge, pulsed streamer discharge (PSD) and atmospheric pressure glow discharge use above principal to generate ozone. In water treatment plants corona discharge technique is popular as it has developed to large scale, commercial production (Alsheyab & Muñoz, 2007).

2.7.5 UV radiation

Solar radiation is electromagnetic (EM) waves emit from sun that ranges from X-rays to radio waves. These X-rays have both wave and particle properties; hence term ‘photon’ is refers to particle characteristic of radiation. Ultra Violet (UV) radiation (from 100 nm to 400 nm) is one important part in the EM spectrum (Figure 2.8) (Badescu, 2008) and can be categorized into four groups (Table 2.12).

(43)

Table 2-12 Distinct bands of UV (Akram, 2005) Band Wavelength UV – A 315 – 400 nm UV – B 280 – 315 nm UV – C 100 – 280 nm UV – Vacuum 100 – 200 nm

All the distinct wave lengths of UV have photochemical effect on pathogenic microorganisms, but UV– C is the most effective because it is absorbed by proteins, RNA and DNA (Kowalski, 2009), which will disrupt the single strand of RNA or double strands of DNA (Figure 2.9) resulting in inactivation of microorganisms. UV sensitivity of pathogenic microorganisms can be arranged as following sequence:

Bacteria = Protozoa > Viruses > Bacteria spores > Algae (Staff, 2008).

Figure 2.9 UV disrupts nucleotides in DNA (LIT UV elektro, n.d.)

Generally mercury lamps (low pressure or high pressure) are used for UV disinfection. Emission of UV decreases with fouling on the quartz covers of the lamps (Bitton, 2014) therefore regular cleaning and maintenance of the UV system is required (Solomon, 1998 ).

(44)

Figure 2.10 UV reactor installment (Ministry of Health, 2010 )

In the presence of organic matter, UV light produces hydrogen peroxide which also contributes to disinfection (Matsuo, 2001). UV is paired with chlorine disinfection because chlorine provides residual disinfection and UV will deactivate microbes and spores unaffected by chlorine disinfection (Ray & Jain, 2014).

Table 2-13 Comparison of drinking water disinfectants (McGuire, 2016)

Disinfectant Advantages Disadvantages

Elemental chlorine (Cl2) - the most commonly use form of chlorine  low cost

 the most energy efficient of all chlorine based disinfectants

 unlimited shelf-life

 comes as pressurized gas- need special care of handling  additional regulation requirements (safety and health management standards) Sodium Hypochlorite (NaOCl)  a solution –less hazardous and easy to handle  less training requirements  less regulations requirements  limited shelf-life- degrade  corrosive

(45)

Hypochlorite [Ca(OCl)2]

 Less training requirement

[Ca(OCl)2] can cause feeding problems  Higher cost compared

to elemental chlorine  Explosive hazards  Can contain chlorate,

chlorite while manufacturing Chloromine

(monochloromine) (NH2Cl)

 More stable residual than free chlorine  Fewer dose requires –

less odor and taste  Excellent secondary disinfectant  Protects distributed water  Weaker disinfectant and oxidant

 Longer contact times  May produce nitrosamine  May contribute in nitrification  Ammonia and chloromines toxic to fish- threats to aquatic life

 Not good for kidneys Chlorine dioxide

(ClO2)

 Reasonably effective against cryptosporidium  Fast inactivating Gardia  Active in wide pH range  Does not form

chlorinated Dissolved by-products

 Effective in taste and odor controlling  Oxidize manganese

 May form chlorite, chlorate  Highly volatile residual  Requires on-site generation  Requires additional training

 Higher operation cost 

Ozone  Strongest disinfectant

available

 Does not directly produce by-products  Effective against cryptosporidium  Require higher technical knowledge  No residual disinfection  Forms by-products  Higher cost

 Difficult to control & monitor

Ultra Violet

radiation

 Effective against most viruses, protozoa and spores

 No residual disinfection

(46)

 No chemical generation or handling needed  Effective against cryptosporidium  Protolyzes nitrosamines for some microorganisms  Difficult to monitor  Usually requires additional treatments/ pre-treatments

2.8 Contaminant removal

Dissolved impurities found in water are commonly ions (cations, anions), heavy metals, gases and disinfectants (Seneviratne, 2007).

Table 2-14 Common ions found in water (Seneviratne, 2007)

Cations Anions Calcium (Ca2+) Magnesium (Mg2+ ) Sodium (Na+) Potassium (K+) Iron (Fe2+) Manganese (Mn2+) Chloride (Cl-) Sulphate (SO42-) Nitrates (NO3-)

Iron and manganese are frequently found cations. Iron concentration can be between 1 mg/L – 100 mg/L and manganese concentration up to 3 mg/L in source water. The aesthetic quality of the water is affected when the iron concentration is higher than 0.5 mg/L and manganese concentration is greater than 0.1 mg/L. There are two common oxidation states/valence states for iron: iron (II) and iron (III) and manganese has oxidation states of (II), (III), (IV), (VI) and (VII). Iron (VI), (V), and (VI) are less common due to low stability (Mackay, 2002; Sommerfield, 1999). Iron (III) oxide (Fe2O3) is insoluble in water (Housecroft,

2012). Permanganate (MnO4-) is another common form of manganese which

soluble in water but when it is reduced to green manganate (MnO42-) it is

insoluble. The most thermodynamically stable state of Manganese is Mn2+ and it

forms all the regularly found salts of manganese including nitrates, chlorides and sulphates (Rayner-Canham, 2014). Iron and manganese can be present in water in

References

Related documents

 Veterans who receive a service related disability from an injury or disease during active military duty may qualify for VA Medical Disability Compensation and free medical care.

preparedness of candidates; section three asked questions level of education and work experience practitioners perceive to be required for the different management

“Gourmet Bakers and Sweets” is the largest food retail chain of Lahore. It is based in Lahore, the second largest city of Pakistan known for its traditional foods and passion

The system relies on a bag of features approach using multiple code- books where new color and textural features are pro- posed for describing skin cancer lesions efficiently,

Ethnic concentration relates to racial harassment through at least three channels: hostility in attitudes of majority individuals that find expression in harassment behaviour,

a–e Mean value ± standard deviation; values without common superscripts within the same column were significantly different ( p &lt; 0.05). In addition, the optimal HLB

In general, the results of this study are consistent with previous research on the prediction of pilot training success in two ways: (a) fluid intelligence remains one of

Three types of cogeneration technologies ((Micro- Turbines (MT), Internal Combustion Engines (ICE), Solid Oxide Fuel Cells (SOFC)), and two types of solar